Disposable insert, and use thereof in a method for manufacturing an airfoil

ABSTRACT

Disclosed herein too is a method of forming an integral casting core comprising adding a disposable insert to a metal core die; disposing a slurry into the metal core die; wherein the slurry comprises ceramic particles; firing the slurry to form a integral casting core; and removing the disposable insert from the integral casting core.

BACKGROUND

This disclosure relates to disposable inserts and uses thereof in amethod for manufacturing an airfoil.

Components having complex geometry, such as components having internalpassages and voids therein, are difficult to cast using currentlyavailable methods. The tooling used for the manufacture of such parts isboth expensive and time consuming, often requiring a large lead-time.This situation is exacerbated by the nature of conventional moldscomprising a shell and one or more separately formed ceramic cores. Theceramic cores are prone to shift during casting, leading to low castingtolerances and low casting efficiency (yield). Examples of componentshaving complex geometries that are difficult to cast using currentlyavailable methods, include hollow airfoils for gas turbine engines, andin particular relatively small, double-walled airfoils. Examples of suchairfoils for gas turbine engines include rotor blades and stator vanesof both turbine and compressor sections, or any parts that need internalcooling.

In current methods for casting hollow parts, a ceramic core and shellare produced separately. The ceramic core (for providing the hollowportions of the hollow part) is first manufactured by pouring a slurrythat comprises a ceramic into a metal core die. After curing and firing,the slurry is solidified to form the ceramic core. The ceramic core isthen encased in wax and a ceramic shell is formed around the waxpattern. The wax that encases the ceramic core is then removed to form aceramic mold in which a metal part may be cast. These current methodsare expensive, have long lead-times, and have the disadvantage of lowcasting yields due to lack of reliable registration between the core andshell that permits movement of the core relative to the shell during thefilling of the ceramic mold with molten metal. In the case of hollowairfoils, another disadvantage of such methods is that any holes thatare desired in the casting are formed in an expensive, separate stepafter forming the cast part, for example, by electron dischargemachining (EDM) or laser drilling.

Development time and cost for airfoils are often increased because suchcomponents generally require several iterations, sometimes while thepart is in production. To meet durability requirements, turbine airfoilsare often designed with increased thickness and with increased coolingairflow capability in an attempt to compensate for poor castingtolerance, resulting in decreased engine efficiency and lower enginethrust. Improved methods for casting turbine airfoils will enablepropulsion systems with greater range and greater durability, whileproviding improved airfoil cooling efficiency and greater dimensionalstability.

Double wall construction and narrow secondary flow channels in modernairfoils add to the complexity of the already complex ceramic cores usedin casting of turbine airfoils. Since the ceramic core identicallymatches the various internal voids in the airfoil which represent thevarious cooling channels and features it becomes correspondingly morecomplex as the cooling circuit increases in complexity. The double wallconstruction is difficult to manufacture because the conventional coredie cannot be used to form a complete integral ceramic core. Instead,the ceramic core is manufactured as multiple separate pieces and thenassembled into the complete integral ceramic core. This method ofmanufacture is therefore a time consuming and low yielding process.

Accordingly, there is a need in the field to have an improved processthat accurately produces the complete integral ceramic core for doublewall airfoil casting.

SUMMARY

Disclosed herein is a method of forming an integral casting corecomprising adding a disposable insert to a metal core die; disposing aslurry in to the metal core die; wherein the slurry comprises ceramicparticles; and firing the slurry to form a integral casting core;wherein the disposable insert is removed from the integral casting coreduring the firing of the slurry.

Disclosed herein too is a method comprising adding a disposable insertto a metal core die; wherein the disposable insert comprises a wax;disposing a slurry in to the metal core die; wherein the slurrycomprises ceramic particles; firing the slurry in a first firing processto form a integral casting core; wherein the disposable insert isremoved from the integral casting core during the firing of the slurry;disposing the integral casting core into a wax die; wherein the wax diecomprises a metal surface; injecting a wax into the wax die to form awax component; immersing the wax component into a slurry to form anouter shell; and firing the wax component with the outer shell in asecond firing process to form a ceramic shell; removing the wax from theouter shell and the wax component; disposing a molten metal into theouter shell; and removing the outer shell to yield a molded component.

Disclosed herein too is a metal core die comprising a cured ceramic coredefining a plurality of channels for a double-walled airfoil; and adisposable insert defining a main sidewall, an internal wall, or acombination comprising at least one of a main sidewall and an internalwall.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is an exemplary schematic of a double wall turbine airfoil thatcan be manufactured by using a disposable insert;

FIG. 2 depicts an exemplary embodiment of a metal core die comprising acured ceramic core and the disposable insert;

FIG. 3 depicts the cured ceramic core, which is then fired to form asolidified ceramic core called an integral casting core;

FIG. 4 depicts a wax die that includes the integral casting core;

FIG. 5 depicts a ceramic shell created by the immersion of a wax airfoilin a ceramic slurry; and

FIG. 6 is an exemplary depiction showing the airfoil (molded component)after removal of the ceramic shell and the integral casting core.

DETAILED DESCRIPTION

The use of the terms “a” and “an” and “the” and similar references inthe context of describing the invention (especially in the context ofthe following claims) are to be construed to cover both the singular andthe plural, unless otherwise indicated herein or clearly contradicted bycontext. The modifier “about” used in connection with a quantity isinclusive of the stated value and has the meaning dictated by thecontext (e.g., it includes the degree of error associated withmeasurement of the particular quantity). All ranges disclosed herein areinclusive of the endpoints, and the endpoints are independentlycombinable with each other.

Disclosed herein is a method of manufacturing a component by using adisposable insert during the process of manufacturing a ceramic core.The ceramic core is further used to obtain a casting of the component.The component can comprise a metal, a ceramic or an organic polymer.

The use of a disposable insert is advantageous in that it decreases timebetween iterations in casting ceramic cores, and reduces productionlead-time. The disposable insert also provides for the production of acomplete integral ceramic core without the assembly of a plurality ofsmaller ceramic cores. The disposable insert can be advantageously usedto manufacture turbine airfoils. The disposable insert generally impartssimple configurations to the internal or external portions of theairfoil. It can be mass-produced by process such as rapid prototyping.As will be explained in detail below, the insert is removable after thecore die is opened.

In one embodiment, the method comprises manufacturing a first disposableinsert. The disposable insert is used in conjunction with the metal coredie to create an integral casting core die prior to the injection of aslurry into the metal core die. After disposing the disposable insertinto the metal core die, the opposing portions of the metal core die arebrought together to be in intimate contact with one another and sealed.A slurry that comprises a ceramic powder is injected into the metal coredie with the disposable insert disposed therein. Following gelation ofthe ceramic slurry, the resulting cured ceramic core containing theinsert is removed from the metal core die and subjected to a firstfiring process at an elevated temperature. The firing results inconsolidation of the cured ceramic core into a solidified ceramic core.The solidified ceramic core is also termed the integral casting core.During the conversion of the cured ceramic core into the integralcasting core, the disposable insert is also degraded (either thermally,chemically or mechanically) and thus removed.

The solidified ceramic core is then disposed inside a wax die. The waxdie is made from a metal. Wax is injected between the solidified ceramiccore and the metal and allowed to cool. The wax die is then removedleaving behind a wax component with the ceramic core enclosed therein.The wax component is then subjected to an investment casting processwherein it is repeatedly immersed into a ceramic slurry to form aceramic slurry coat whose an inner surface corresponds in geometry tothe outer surface of the desired component. The wax component disposedinside the ceramic slurry coat is then subjected to a second firingprocess wherein the wax is removed leaving behind a ceramic mold. Moltenmetal may then be poured into the ceramic mold to create a desired metalcomponent. As noted above, the component can be a turbine component suchas, for example, a turbine airfoil.

With reference now to the FIG. 1, an exemplary double wall turbineairfoil 100 comprises a main sidewall 12 that encloses the entireturbine airfoil. The airfoil depicted in FIG. 1 is illustrative, and theinvention is not limited a specific airfoil configuration. As may beseen in the FIG. 1, the main sidewall 12 comprises a leading edge and atrailing edge. Within the main sidewall 12 is a thin internal wall 14.The main sidewall 12 and the thin internal wall 14 (or partition wall)together form the double wall. As may be seen, the airfoil comprises aplurality of channel partition ribs 13, 15, 17, 19 and 21. The doublewall construction is formed between channel partition ribs 17, 19 and 21whose ends are affixed to the main sidewalls. As can be seen in the FIG.1, there are a plurality of channels (also termed impingement cavities)16, 18, 20, 22, 24, 26, 28, 30 and 32 formed between the main sidewall12, the ribs and the thin internal wall 14. The channels permit the flowof a fluid such as air to effect cooling of the airfoil. There are anumber of impingement cross-over holes disposed in the ribs such as theleading edge impingement cross-over holes 2, the mid-circuit double wallimpingement cross over holes 4, 6, and the trailing edge impingementcross-over holes 8 through which air can also flow to effect a coolingof the airfoil.

As may be seen in the FIG. 1, the exemplary double wall airfoilcomprises four impingement cavities 22, 24, 26 and 28 in the mid-chordregion. The impingement cavities 22, 24, 26 and 28 are formed betweenthe main sidewall 12 and the thin internal wall 14. In one embodiment,any portion of the airfoil, such as, for example, the main sidewall 12,the thin internal wall 14, or the channel partition ribs 13, 15, 17, 19and 21 may be manufactured via the use of a sacrificial die (hereinaftera disposable insert). In an exemplary embodiment depicted in thefollowing figures, the thin internal wall 14 may be manufactured via theuse of a disposable insert.

With reference now to the FIG. 2, which depicts an exemplary embodimentof this disclosure, a metal core die 50 comprising the cured ceramiccore 40 and the disposable insert 60 is shown. In accomplishing theembodiment depicted in the FIG. 2, a disposable insert 60 comprising awax is disposed in the metal core die 50. The disposable insert 60 maycomprise a polymer or a wax-polymer composite in lieu of the wax, ifdesired. The metal core die 50 is closed or sealed and a slurrycomprising ceramic particles is then poured into the metal core die 50.The closing or sealing of the constituent parts (not shown) of the metalcore die 50 prohibits leakage of slurry from the die 50. The slurry isthen cured to form a cured ceramic core 40. The cured ceramic core 40surrounds the disposable insert 60.

As can be seen in the FIG. 3, the cured ceramic core 40 is then fired toform a solidified ceramic core called the integral casting core 90.During or after the firing, the disposable insert 60 can be removed. Ifthe disposable insert 60 is removed during the firing, it is generallymelted away or thermally degraded.

In another embodiment, the disposable insert 60 can be removed after thefiring to yield the integral casting core 90. This generally involvesthe use of chemicals or mechanical methods to remove the disposableinsert 60. In this embodiment, the act of removing the disposable insertusing a chemical generally involves dissolution or degradation of theorganic polymer used as a binder in the disposable insert. The act ofremoving the disposable insert using a mechanical method generallyinvolves abrasion.

Following the removal of the disposable insert the integral casting core90 is inserted into a wax die 92 as depicted in the FIG. 4. The wax die92 has an inner surface 94 that corresponds to the desired outer surfaceof the turbine airfoil. Molten wax 96 is then poured into the wax die asshown in the FIG. 4. Upon solidification of the wax, the wax airfoil 102shown in the FIG. 5 is removed from the wax die 92 and repeatedlyimmersed in a ceramic slurry to create a ceramic shell 98.

The wax present in the wax airfoil 102 is then removed by melting it andpermitting it to flow out of the ceramic shell 98 that comprises theintegral casting core 90. After the wax is removed a molten metal,ceramic or polymer may be poured into the ceramic shell 98 thatcomprises the integral casting core 90. In an exemplary embodiment, amolten metal is poured into the ceramic shell 98 to form the airfoil asdepicted in the FIG. 6. FIG. 6 shows the ceramic shell 98 after themolten metal is disposed in it. Following the cooling and solidificationof the metal, the ceramic shell 98 is broken to remove the desiredairfoil. The integral casting core is then removed via chemicalleaching.

Thus the disposable insert can advantageously be used to manufactureairfoils having a double wall design. In the aforementioned FIGS. 1 to6, the disposable insert was used to form the partition wall 14 in thedouble wall blade design. The disposable inserts can be used in themetal core dies in order to produce an integral casting core withoutfurther assembly. The use of a disposable insert therefore produceshigher yields and lowers costs.

In one exemplary embodiment, a plurality of disposable inserts can beused in the integral casting core. A plurality is defined as any numbergreater than 1.

The disposable insert 60 is generally manufactured from an insertcasting composition that comprises an organic polymer. The organicpolymer can be selected from a wide variety of thermoplastic polymers,thermosetting polymers, blends of thermoplastic polymers, or blends ofthermoplastic polymers with thermosetting polymers. The organic polymercan comprise a homopolymer, a copolymer such as a star block copolymer,a graft copolymer, an alternating block copolymer or a random copolymer,ionomer, dendrimer, or a combination comprising at least one of theforegoing types of organic polymers. The organic polymer may also be ablend of polymers, copolymers, terpolymers, or the like, or acombination comprising at least one of the foregoing types of organicpolymers.

Examples of suitable organic polymers are natural and synthetic waxesand fatty esters, polyacetals, polyolefins, polyesters, polyaramides,polyarylates, polyethersulfones, polyphenylene sulfides,polyetherimides, polytetrafluoroethylenes, polyetherketones, polyetheretherketones, polyether ketone ketones, polybenzoxazoles, polyacrylics,polycarbonates, polystyrenes, polyamides, polyamideimides, polyarylates,polyurethanes, polyarylsulfones, polyethersulfones, polyarylenesulfides, polyvinyl chlorides, polysulfones, polyetherimides, or thelike, or a combinations comprising at least one of the foregoingpolymeric resins.

Blends of organic polymers can be used as well. Examples of suitableblends of organic polymers include acrylonitrile-butadiene styrene,acrylonitrile-butadiene-styrene/nylon,polycarbonate/acrylonitrile-butadiene-styrene, polyphenyleneether/polystyrene, polyphenylene ether/polyamide,polycarbonate/polyester, polyphenylene ether/polyolefin, andcombinations comprising at least one of the foregoing blends of organicpolymers.

Exemplary organic polymers are acrylonitrile-butadiene styrene (ABS),natural and synthetic waxes and fatty esters, and ultraviolet (UV))cured acrylates. Examples of suitable synthetic wax compounds aren-alkanes, ketones, secondary alcohols, beta-diketones, monoesters,primary alcohols, aldehydes, alkanoic acids, dicarboxylic acids,omega-hydroxy acids having about 10 to about 38 carbon atoms. Examplesof suitable natural wax compounds are animal waxes, vegetal waxes, andmineral waxes, or the like, or a combination comprising at least one ofthe foregoing waxes. Examples of animal waxes are beeswax, Chinese wax(insect wax), Shellac wax, whale spermacetti, lanolin, or the like, or acombination comprising at least one of the foregoing animal waxes.Examples of vegetal waxes are carnauba wax, ouricouri wax, jojoba wax,candelilla wax, Japan wax, rice bran oil, or the like, or a combinationcomprising at least one of the foregoing waxes. Examples of mineralwaxes are ozocerite, Montan wax, or the like, or a combinationcomprising at least one of the foregoing waxes.

As noted above, the disposable insert can be manufactured fromthermosetting or crosslinked polymers such as, for example, UV curedacrylates. Examples of crosslinked polymers include radiation curable orphotocurable polymers. Radiation curable compositions comprise aradiation curable material comprising a radiation curable functionalgroup, for example an ethylenically unsaturated group, an epoxide, andthe like. Suitable ethylenically unsaturated groups include acrylate,methacrylate, vinyl, allyl, or other ethylenically unsaturatedfunctional groups. As used herein, “(meth)acrylate” is inclusive of bothacrylate and methacrylate functional groups. The materials can be in theform of monomers, oligomers, and/or polymers, or mixtures thereof. Thematerials can also be monofunctional or polyfunctional, for example di-,tri-, tetra-, and higher functional materials. As used herein, mono-,di-, tri-, and tetrafunctional materials refers to compounds having one,two, three, and four radiation curable functional groups, respectively.

Exemplary (meth)acrylates include methyl acrylate, tert-butyl acrylate,neopentyl acrylate, lauryl acrylate, cetyl acrylate, cyclohexylacrylate, isobornyl acrylate, phenyl acrylate, benzyl acrylate, o-toluylacrylate, m-toluyl acrylate, p-toluyl acrylate, 2-naphthyl acrylate,4-butoxycarbonylphenyl acrylate, 2-methoxy-carbonylphenyl acrylate,2-acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxy-propylacrylate, ethyl methacrylate, n-butyl methacrylate, sec-butylmethacrylate, isobutyl methacrylate, propyl methacrylate, isopropylmethacrylate, n-stearyl methacrylate, cyclohexyl methacrylate,4-tert-butylcyclohexyl methacrylate, tetrahydrofurfuryl methacrylate,benzyl methacrylate, phenethyl methacrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate, andthe like, or a combination comprising at least one of the foregoing(meth)acrylates.

The organic polymer may also comprise an acrylate monomer copolymerizedwith another monomer that has an unsaturated bond copolymerizable withthe acrylate monomer. Suitable examples of copolymerizable monomersinclude styrene derivatives, vinyl ester derivatives, N-vinylderivatives, (meth)acrylate derivatives, (meth)acrylonitrilederivatives, (meth)acrylic acid, maleic anhydride, maleimidederivatives, and the like, or a combination comprising at least one ofthe foregoing monomers.

An initiator can be added to the insert casting composition in order toactivate polymerization of any monomers present. The initiator may be afree-radical initiator. Examples of suitable free-radical initiatorsinclude ammonium persulfate, ammonium persulfate andtetramethylethylenediamine mixtures, sodium persulfate, sodiumpersulfate and tetramethylethylenediamine mixtures, potassiumpersulfate, potassium persulfate and tetramethylethylenediaminemixtures, azobis[2-(2-imidazolin-2-yl) propane] HCl (AZIP), andazobis(2-amidinopropane) HCl (AZAP), 4,4′-azo-bis-4-cyanopentanoic acid,azobisisobutyramide, azobisisobutyramidine.2HCl,2-2′-azo-bis-2-(methylcarboxy) propane, 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone, 2-hydroxy-2-methyl-1-phenyl-1-propanone,or the like, or a combination comprising at least one of theaforementioned free-radical initiators. Some additives or comonomers canalso initiate polymerization, in which case a separate initiator may notbe desired. The initiator can control the reaction in addition toinitiating it. The initiator is used in amounts of about 0.005 wt % andabout 0.5 wt %, based on the weight of the insert casting composition.

Other initiator systems, in addition to free-radical initiator systems,can also be used in the insert casting composition. These includeultraviolet (UV), x-ray, gamma-ray, electron beam, or other forms ofradiation, which could serve as suitable polymerization initiators. Theinitiators may be added to the insert casting composition either duringthe manufacture of the insert casting composition or just prior tocasting.

Dispersants, flocculants, and suspending agents can also be optionallyadded to the insert casting composition to control the flow behavior ofthe composition. Dispersants make the composition flow more readily,flocculants male the composition flow less readily, and suspendingagents prevent particles from settling out of composition. Theseadditives are generally used in amounts of about 0.01 to about 10 wt %,of the total weight of the ceramic or metal powder in the insert castingcomposition.

As noted above, the integral casting core may be further used formolding metal castings. In one exemplary embodiment, the disposableinserts may be used for manufacturing turbine components. These turbinecomponents can be used in either power generation turbines such as gasturbines, hydroelectric generation turbines, steam turbines, or thelike, or they may be turbines that are used to facilitate propulsion inaircraft, locomotives, or ships. Examples of turbine components that maybe manufactured using disposable inserts are stationary and/or rotatingairfoils. Examples of other turbine components that may be manufacturedusing disposable inserts are seals, shrouds, splitters, or the like.

Disposable inserts have a number of advantages. They can be massproduced if desired and widely used in casting operations for themanufacture of turbine airfoils. The disposable insert can be massproduced at a low cost. The disposable insert can be manufactured insimple or complex shapes. The use of a disposable insert can facilitatethe production of the integral casting core without added assembly ormanufacturing. This results in lower costs for the manufacturing ofcomponents having intricate internal designs.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention.

1. A method of forming an integral casting core comprising: adding adisposable insert to a metal core die, wherein the disposable insertdefines a partition wall in a double wall airfoil; disposing a slurryinto the metal core die; wherein the slurry comprises ceramic particles;firing the slurry to form an integral casting core, wherein the integralcasting core is formed via a single step of disposing the slurry intothe metal core die; and removing the disposable insert from the integralcasting core.
 2. The method of claim 1, wherein the removal of thedisposable insert is accomplished via chemical dissolution, chemicaldegradation, mechanical abrasion, melting, thermal degradation or acombination comprising at least one of the foregoing methods ofremoving.
 3. The method of claim 1, wherein the disposable insert ismanufactured by a rapid prototyping process.
 4. (canceled)
 5. The methodof claim 1, further comprising curing the slurry to form a cured ceramiccore.
 6. The method of claim 5, wherein the curing of the slurry isconducted prior to the firing of the slurry.
 7. The method of claim 1,wherein the removal of the disposable insert comprises degrading thedisposable insert.
 8. The method of claim 1, further comprisingdisposing the integral casting core into a wax die; wherein the wax diecomprises a metal.
 9. The method of claim 8, further comprisinginjecting a wax into the wax die to form a wax component.
 10. The methodof claim 9, further comprising immersing the wax component into a slurryto form an outer shell; and firing the wax component with the outershell to form a ceramic shell.
 11. The method of claim 9, wherein theslurry comprises a ceramic.
 12. The method of claim 9, furthercomprising removing the wax from the outer shell and the wax component.13. The method of claim 12, further comprising disposing a molten metalinto the outer shell.
 14. The method of claim 13, further comprisingremoving the outer shell and an integral casting core to yield a moldedcomponent.
 15. A double wall airfoil comprising a partition wallmanufactured by the method of claim
 1. 16. The article of claim 15,wherein the double wall airfoil is a turbine component.
 17. A methodcomprising: adding a disposable insert to a metal core die; wherein thedisposable insert comprises a wax and defines a partition wall in adouble wall airfoil; disposing a slurry in to the metal core die;wherein the slurry comprises ceramic particles; firing the slurry in afirst firing process to form an integral casting core; wherein thedisposable insert is removed from the integral casting core during thefiring of the slurry, and wherein the integral casting core is formedvia a single step of disposing the slurry into the metal core die;disposing the integral casting core into a wax die; wherein the wax diecomprises a metal surface; injecting a wax into the wax die to form awax component; immersing the wax component into a slurry to form anouter shell; firing the wax component with the outer shell in a secondfiring process to form a ceramic shell; removing the wax from the outershell and the wax component; disposing a molten metal into the outershell; and removing the outer shell to yield a molded component.
 18. Themethod of claim 17, wherein the molded component is a turbine airfoil.19. The method of claim 17, wherein the disposable insert comprises awax.
 20. The method of claim 17, wherein the disposable insert comprisesan organic polymer.
 21. The method of claim 20, wherein the organicpolymer is a thermoplastic polymer, a thermosetting polymer, a blend ofthermoplastic polymers, or blends of thermoplastic polymers withthermosetting polymers.
 22. The method of claim 20, wherein the organicpolymer is a homopolymer, a copolymer, a star block copolymer, a graftcopolymer, an alternating block copolymer, a random copolymer, anionomer, a dendrimer, or a combination comprising at least one of theforegoing types of organic polymers.
 23. The method of claim 22, whereinthe organic polymer is a blend of polymers, copolymers, terpolymers, ora combination comprising at least one of the foregoing types of organicpolymers.
 24. A metal core die comprising: a cured ceramic core defininga plurality of channels for a double-walled airfoil, wherein thedouble-walled airfoil comprises a main sidewall, a plurality of channelpartition ribs extending between the main sidewall, and an internal wallextending between at least a subset of the partition ribs; and adisposable insert defining the main sidewall, the internal wall, or acombination comprising at least one of the main sidewall and theinternal wall.
 25. The metal core die of claim 24, wherein thedisposable insert defines an impingement cross-over hole.
 26. The metalcore die of claim 24, wherein the internal wall is a partition wall. 27.The metal core die of claim 24, wherein the disposable insert comprisesa wax.
 28. The method of claim 24, wherein the disposable insertcomprises an organic polymer.